Carnage
08-12-2013, 04:42 PM
#46
Former Vendor
Certainly, if the lift is not increased but duration is increased, one can create a valve lift profile that is a lot easier on the lifters and lobes and requires less spring load, for the same rpm. It's the short duration high lift cams that are hard, and I think most people looking for performance 928 camshafts are looking for longer than stock duration.
Agreed.
The negative accelerations not being a concern for out engines leads me to the following question: Why do you need these high spring rate springs then? It's my understanding that the high spring rates are primarily needed to offset the negative accelerations on all cams, not just racing cams.
The stock 928 valve spring is barely adequate [and some think it is inadequate (including me) for the stock GT Camshaft profile]. Those heavy, oil filled lifters have a huge mass. Certainly the stock springs are inadequate beyond the stock rpm range. The "mild" step in valve spring tension from the stock spring to the 944S2 spring is very reasonable. To get a "smaller" step would require an "aftermarket" spring. I've pretty well covered why I like to use "stock" Porsche springs and not play around with "aftermarket springs.
More specifically and making this concrete, 944 S2 springs are something like 300 lbf/inch rate. Why those 300 lbf/inch springs instead of the gentler 928 S4 springs with 225 lbf/inch spring rate if the negative acceleration is nowhere close to the limit? Is it just that for the 928 the priority is to find a spring that can accommodate the maximum lift without coil bind while simultaneously giving a bounce-free seated load, while the spring load on/near the nose is irrelevant (by being too high for all these springs mentioned here)?
Did not say that the negative acceleration was not near the limit (clearly I think it is, on certain of even the stock cams). Certainly, by changing out the lifter to something besides that "virtual rock" that is used stock significantly reduces this problem, as I mentioned.
I didn't think it would be possible to run a tangent cam lobe (flat surface connecting the base circle and the nose circle) on a flat follower. The reason why I thought this would not be possible is because the lubrication would not work with the large contact area early in the lift. Perhaps I have misunderstood this issue, or what you meant by flat cutting the ramp or the flank.
Exactly what I meant. Porsche indeed did this very thing, on the Cup Race engines....hydraulic lifter and all....so very possible.
Agreed.
The negative accelerations not being a concern for out engines leads me to the following question: Why do you need these high spring rate springs then? It's my understanding that the high spring rates are primarily needed to offset the negative accelerations on all cams, not just racing cams.
The stock 928 valve spring is barely adequate [and some think it is inadequate (including me) for the stock GT Camshaft profile]. Those heavy, oil filled lifters have a huge mass. Certainly the stock springs are inadequate beyond the stock rpm range. The "mild" step in valve spring tension from the stock spring to the 944S2 spring is very reasonable. To get a "smaller" step would require an "aftermarket" spring. I've pretty well covered why I like to use "stock" Porsche springs and not play around with "aftermarket springs.
More specifically and making this concrete, 944 S2 springs are something like 300 lbf/inch rate. Why those 300 lbf/inch springs instead of the gentler 928 S4 springs with 225 lbf/inch spring rate if the negative acceleration is nowhere close to the limit? Is it just that for the 928 the priority is to find a spring that can accommodate the maximum lift without coil bind while simultaneously giving a bounce-free seated load, while the spring load on/near the nose is irrelevant (by being too high for all these springs mentioned here)?
Did not say that the negative acceleration was not near the limit (clearly I think it is, on certain of even the stock cams). Certainly, by changing out the lifter to something besides that "virtual rock" that is used stock significantly reduces this problem, as I mentioned.
I didn't think it would be possible to run a tangent cam lobe (flat surface connecting the base circle and the nose circle) on a flat follower. The reason why I thought this would not be possible is because the lubrication would not work with the large contact area early in the lift. Perhaps I have misunderstood this issue, or what you meant by flat cutting the ramp or the flank.
Exactly what I meant. Porsche indeed did this very thing, on the Cup Race engines....hydraulic lifter and all....so very possible.
08-12-2013, 05:53 PM
#47
The weight of what the spring is being asked to move cannot be understated. Get into the software and find out how much the usable RPM changes when you reduce the weight of the assembly.
08-12-2013, 06:06 PM
#48
Nordschleife Master
Isn't that just a proportional relationship between required spring load and the reciprocating mass, and an inversely proportional relationship between square root of maximum safe rpm and reciprocating mass? That's what they taught in my high school, is there more of a trick to it?
08-12-2013, 06:12 PM
#49
Former Vendor
I had a set of heads which came to me with titanium retainers, which I had at Randy Aase's (very smart guy....understands the "big" picture) shop for some special valve work, that I could not do, in house.
He laughed very loudly at the titanium retainers: "What a waste of time and money, with those stock lifters."
08-12-2013, 06:17 PM
#50
Isn't that just a proportional relationship between required spring load and the reciprocating mass, and an inversely proportional relationship between square root of maximum safe rpm and reciprocating mass? That's what they taught in my high school, is there more of a trick to it?
And when I was in Undergrad and then my MBA, I did get into math - and was SUCCESSFUL with getting the female tail. The math, however, was economics and statistics, and the tail was much easier...
Wait, never mind.
I am not sure how proportional the relationship it is mathematically. And using the software I am sure you know I am using, does not always mean its showing me everything. Boost pressurizing the intake or exhaust back pressure can change the dynamics that the valve will be moving under.
08-12-2013, 06:21 PM
#51
By 20+ grams, with a lightweight lifter.....30% of the total lifter weight!
I had a set of heads which came to me with titanium retainers, which I had at Randy Aase's (very smart guy....understands the "big" picture) shop for some special valve work, that I could not do, in house.
He laughed very loudly at the titanium retainers: "What a waste of time and money, with those stock lifters."
I had a set of heads which came to me with titanium retainers, which I had at Randy Aase's (very smart guy....understands the "big" picture) shop for some special valve work, that I could not do, in house.
He laughed very loudly at the titanium retainers: "What a waste of time and money, with those stock lifters."
08-13-2013, 07:56 PM
#52
anyone have the part numbers for the 944s2 springs or the porsche racing ones? i cant seem to find them. i at the point of getting my S3heads done and ready for Colins cams. but springs busting is not in the cards.
08-13-2013, 08:28 PM
#53
Three Wheelin'
^^^^ I'm curious to know if those S2 springs or racing springs would work with S3 heads/valve train.
The 85-86 valve springs are shorter and different from the springs in the S4 engines.
Edit: I think I'm wrong the springs are the same, but still interested in knowing if s2 springs can be installed.
These are the S2 springs=944 105 907 01:
http://www.mailordercentral.com/928i...105%20907%2001
http://www.pelicanparts.com/cgi-bin/...105-907-01-OEM
The 85-86 valve springs are shorter and different from the springs in the S4 engines.
Edit: I think I'm wrong the springs are the same, but still interested in knowing if s2 springs can be installed.
These are the S2 springs=944 105 907 01:
http://www.mailordercentral.com/928i...105%20907%2001
http://www.pelicanparts.com/cgi-bin/...105-907-01-OEM
Last edited by namasgt; 08-13-2013 at 08:47 PM.
08-14-2013, 05:11 AM
#54
Rennlist Member
Join Date: Feb 2011
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If you are looking for a racing spring that will not break I have a dual spring being used for more than 35 years in numerous applications. Will fit right into the S4 head but the seats have to be cut down in diameter for the outer spring (from .894" to .854").
Seated pressure @ 1.398" (35,5 mm) 70 lbs.
At .437" of lift 221 lbs.
At .500" of lift 242 lbs.
Coil bind at .768" (19,5mm).
Price $ 12.00 each. Will ship worldwide.
Ake Jonsson Engineering, Sweden
Seated pressure @ 1.398" (35,5 mm) 70 lbs.
At .437" of lift 221 lbs.
At .500" of lift 242 lbs.
Coil bind at .768" (19,5mm).
Price $ 12.00 each. Will ship worldwide.
Ake Jonsson Engineering, Sweden
08-14-2013, 10:59 AM
#55
Tell us more about that cam in you avatar pic
08-17-2013, 03:55 AM
#56
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Join Date: Feb 2011
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My avatar picture is showing a S4 intake camshaft having an adjustable chain sprocket making it possible to individually time the cams. The lobe separation angle and with it the degrees of overlap can be altered any way you like. The moveable chain sprocket is locked with a heavy duty clamp. The experts can also see the profile of the lobes has been altered for more duration and lift.
Ake Jonsson Engineering, Sweden
Ake Jonsson Engineering, Sweden
08-17-2013, 04:08 AM
#57
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Join Date: Feb 2011
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Tuomo asked me to measure the stock S4 valve spring pressure once more as the data I provided him did not conform with what he had got from Louise Ott. I thought I might share so you can compare with other springs mentioned in this thread. I do not have a precision scale but the result is pretty accurate.
According to the factory repair manual the installed height is intake 35,5 mm and exhaust 34,5 mm with a tolerance of +0,5mm.
However the measurement shall be taken with the top retainer which is 2mm thick in place, making the actual valve spring installed height 33,5 mm and 32,5 mm respectively. I think here Louie Ott probably made a mistake. The reason why the exhaust spring is installed 1mm shorter is the exhaust valve lift is 1mm less making the open pressure the same for both intake and exhaust.
Stock S4 Valve Springs measured:
Seated pressure at 33,5 mm (1.319") is 32 kp or 70.5 lbs.
Seated pressure at 32,5 mm (1.280") is 36 kp or 79,5 lbs.
Open pressure at 24,5 mm (.965") is 72 kp or 159 lbs.
Coil bind at 22mm or .866".
Ake Jonsson Engineering, Sweden
According to the factory repair manual the installed height is intake 35,5 mm and exhaust 34,5 mm with a tolerance of +0,5mm.
However the measurement shall be taken with the top retainer which is 2mm thick in place, making the actual valve spring installed height 33,5 mm and 32,5 mm respectively. I think here Louie Ott probably made a mistake. The reason why the exhaust spring is installed 1mm shorter is the exhaust valve lift is 1mm less making the open pressure the same for both intake and exhaust.
Stock S4 Valve Springs measured:
Seated pressure at 33,5 mm (1.319") is 32 kp or 70.5 lbs.
Seated pressure at 32,5 mm (1.280") is 36 kp or 79,5 lbs.
Open pressure at 24,5 mm (.965") is 72 kp or 159 lbs.
Coil bind at 22mm or .866".
Ake Jonsson Engineering, Sweden